In the prime label market, a 44# natural kraft release liner with silicone-coated polypropylene (PP) on one side has been popular because it provided a consistent die-cutting surface, even at high conversion speeds, coupled with reliable release performance.

However, one-side PP-coated products have a propensity to curl and the potential for paper dusting on the non-coated side. Curl reduces throughput efficiencies for both the converter and the end-user — in particular by making it more difficult to butt together for splicing rolls of converted, matrix-stripped labels.

To eliminate these curl and dusting issues, a product was developed that would do so, without sacrificing die-cutting qualities.

First, the properties were identified that a converter and end-user would most appreciate in a release liner:

Optimal caliper for the existing base of rotary die-cutting tools

Optimal die-cutting performance

Minimal bleed-through

Improved layflat and dimensional stability

The same high degree of surface smoothness and consistency as our company's first-generation product, which was used as a control

Competitive cost

The release liner construction that could deliver such characteristics seemed to be a two-sided PP-coated grade. The culmination of development work is a dustfree, two-sided polycoated release liner with greatly improved curl control.

Extensive testing was performed on the new release liner grade's die-cutting properties, evaluating for clean die-cutting through 2.6 mil PP facestock — purposely selected because of the unique die-cutting challenges it presents.

Layflat Improved Tests were conducted using standard clearances for the original liner so that interchangeability would be guaranteed. A commonly used rotary die-cutting clearance was selected and bracketed with ±0.0002 in. clearances. Clean die-cutting was defined as good strike-through without any rough edges, nicks, or burrs. Die-cutting was rated on a scale of 1-10, with 10 being a perfect score.

The new liners also were evaluated for “bleed-through,” which may be defined as strike-through into the release liner. Bleed-through is a concern in converting because of the potential for adhesive flow into the scored liner as well as liner breakage due to the reduced internal strength of the release liner on label applicators.

Bleed-through also was evaluated on a scale of 1-10, where a rating of 10 had no strike-through into the release liner. The goal was to achieve excellent die-cutting with no bleed-through.

An inter-relationship between die-cutting and bleed-through exists, and the perfect balance can be difficult to achieve.

Improved die-cutting results often are achieved at the risk of scoring the liner, causing bleed-through.

Conversely, minimization of bleed-through can result in poor die-cutting performance, with insufficient strike-through and resulting nicks, burrs, or rough edges.

The goal was to engineer a release liner that would accommodate high-end application requirements for both die-cutting and bleed-through using the existing rotary die-cutting tools favored today by converters — thus enabling them to make an easy transition to the second-generation product and eliminate the usual inefficiencies associated with costly changeovers.

The results of the tests on the new liner showed the new product offered die-cutting and bleed-through results equivalent to the control — our first-generation grade — but with significant improvements in layflat (see Figure 1).

The two-sided polycoating also provided freedom from dusting.

In summary, the new liner is believed to provide just what the prime label market wants: a viable two-sides polycoated release liner with superior dimensional stability and no backside dusting issues — and because the liner is “comfortable” with the standard die-cutting tools in use today, it is easy to transition to the new product.